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Download 03&04 ANS LECTURE Sultan Ayoub Meo Sept 2 2012
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ANATOMY AND PHYSIOLOGY OF SYMPATHETIC AND PARASYMPATHETIC NERVOUS SYSTEM Prof. Sultan Ayoub Meo MBBS, Ph.D, FRCP (London, Dublin, Glasgow, Edinburgh) Professor, Department of Physiology, College of Medicine King Saud University, Riyadh, KSA THE AUTONOMIC NERVOUS SYSTEM THE NERVOUS SYSTEM 1. Central Nervous System 2. Peripheral Nervous System 1. Central Nervous System Brain Fore brain: Cerebrum, Diencephalon (Thalamus, Metathalamus, Epithalamus, Hypothalamus and subthalamus Mid brain Hind brain: Pons, Medulla oblongata, Cerebellum Spinal cord THE NERVOUS SYSTEM 2. Peripheral Nervous System: Peripheral Nervous System formed by neurons & their process present in all the regions of the body. It consists of cranial and spinal nerves arising from brain and spinal cord respectively. a) Somatic Nervous System b) Autonomic Nervous System i. Sympathetic nervous system ii. Parasympathetic nervous system THE AUTONOMIC NERVOUS SYSTEM Somatic nervous system: Controls organs under voluntary control (mainly skeletal muscles) Autonomic Nervous System (ANS): Not under voluntary control. It regulates individual organ, visceral functions and homeostasis, known as the visceral or automatic system. Effectors includes cardiac, smooth muscles and glands. Helps to adapt the changes in environment. Adjusts or modifies functions in response to stress such as blood pressure, body temperature, sweating etc. COMPARISON OF AUTONOMIC AND SOMATIC SYSTEMS Somatic system One motor neuron extends from the CNS to skeletal muscle Axons are well myelinated Conduct impulses rapidly COMPARISON OF AUTONOMIC AND SOMATIC MOTOR SYSTEMS Autonomic nervous system Chain of two motor neurons Preganglionic neuron Postganglionic neuron Conduction is slower due to thin or unmyelinated axons Pre-ganglionic Post-ganglionic Ganglion COMPARISON OF AUTONOMIC AND SOMATIC MOTOR SYSTEMS THE AUTONOMIC NERVOUS SYSTEM The ANS is predominantly an efferent system transmitting impulses from the Central Nervous System (CNS) to peripheral organ systems. Its effects include: Control of heart rate and force of contraction Constriction and dilatation of blood vessels Contraction and relaxation of smooth muscle Visual accommodation Secretions from exocrine and endocrine glands. THE AUTONOMIC NERVOUS SYSTEM ANS activated by centers located in the spinal cord, brain stem, hypothalamus and also cerebral cortex especially the limbic cortex can transmit signals to the lower centers, influence autonomic control. ANS operates by visceral reflexes. Subconscious sensory signals from a visceral organ enter the autonomic ganglia, brain stem or hypothalamus and then return subconscious reflex responses directly back to the visceral organ to control its activities. THE AUTONOMIC NERVOUS SYSTEM Sympathetic and parasympathetic systems are consists of myelinated pre-ganglionic fibers which make synaptic connections with un-myelinated postganglionic fibers and then innervate the effector organ These synapses usually occur in clusters called ganglia. THE AUTONOMIC NERVOUS SYSTEM Preganglionic neuron: Cell body in brain or spinal cord Axon is myelinated type fiber that extends to autonomic ganglion Postganglionic neuron: Cell body lies outside the CNS in an autonomic ganglion Axon is unmyelinated type fiber that terminates in a visceral effector THE AUTONOMIC NERVOUS SYSTEM 2 neurons in the efferent pathway. 1st neuron has its cell body in gray matter of brain or spinal cord. Preganglionic neuron. • Synapses with 2nd neuron within an autonomic ganglion. Postganglionic neuron. • Autonomic ganglion has axon which extends to synapse with target tissue. DIFFERENCES IN SYMPATHETIC AND PARASYMPATHETIC DIVISIONS Length of postganglionic fibers Sympathetic – long postganglionic fibers Parasympathetic – short postganglionic fibers Branching of axons Sympathetic axons – highly branched Parasympathetic axons – few branches DIFFERENCES IN SYMPATHETIC AND PARASYMPATHETIC DIVISIONS THE AUTONOMIC NERVOUS SYSTEM THE AUTONOMIC NERVOUS SYSTEM THE AUTONOMIC NERVOUS SYSTEM Subdivision Nerves Employed Sympathetic Parasympath etic Location of Ganglia Chemical Messenger General Function Thoracolumbar Alongside vertebral column Norepinephrine Fight or flight Craniosacral Acetylcholine Conservation of body energy On or near an effector organ THE AUTONOMIC NERVOUS SYSTEM NEUROTRANSMITTERS OF AUTONOMIC NERVOUS SYSTEM Neurotransmitter released by pre-ganglionic axons Acetylcholine for both branches (cholinergic) Neurotransmitter released by postganglionic axons Sympathetic – most release norepinephrine (adrenergic) Parasympathetic – release acetylcholine THE AUTONOMIC NERVOUS SYSTEM Sympathetic: Originate in the thoracic and lumbar regions of the spinal cord (Thoracolumbar) Parasympathetic: Originate from cranial nerves (3rd, 7th, 9th, 10th), and sacral spinal nerves (craniosacral) SEGMENTAL DISTRIBUTION OF THE SYMPATHETIC NERVOUS SYSTEM Sympathetic fibers from cord segment T-1 generally pass up the sympathetic chain to terminate in the head; T-2 to terminate in the neck T-3, T-4, T-5, and T-6 into the thorax T-7, T-8, T-9, T-10, and T-11 into the abdomen T-12, L-1, and L-2 into the legs. DISTRIBUTION OF THE SYMPATHETIC AND PARASYMPATHTIC NERVOUS SYSTEM Blue= Para symp; Red symp FUNCTIONS OF THE SYMPATHETIC AND PARASYMPATHTIC NERVOUS SYSTEM Structure Sympathetic Stimulation Parasympathetic Stimulation Iris (eye muscle) Pupil dilation Pupil constriction Salivary Glands Saliva production reduced Saliva production increased Oral/Nasal Mucosa Mucus production reduced Mucus production increased Heart Heart rate and force increased Heart rate and force decreased Lung Bronchial muscle relaxed Bronchial muscle contracted Stomach Peristalsis reduced Gastric juice secreted; motility increased Small Intes Motility reduced Digestion increased Large Intes Motility reduced Secretions and motility increased Liver Increased conversion of glycogen to glucose Kidney Decreased urine secretion Increased urine secretion Bladder Wall relaxed Sphincter closed Wall contracted Sphincter relaxed THE SYMPATHETIC NERVOUS SYSTEM THE SYMPATHETIC NERVOUS SYSTEM THE SYMPATHETIC NERVOUS SYSTEM FEAR, FIGHT- FLIGHT RESPOSE The sympathetic system enables the body to be prepared for fear, flight or fight Sympathetic responses include an increase in heart rate, blood pressure and cardiac output Diversion of blood flow from the skin and splanchnic vessels to those supplying skeletal muscle Increased pupil size, bronchiolar dilation, contraction of sphincters and metabolic changes such as the mobilisation of fat and glycogen. THE SYMPATHETIC NERVOUS SYSTEM Frequently referred to as the fear, fight or flight response It has a stimulatory effect on organs and physiological systems, responsible for rapid sensory activity (pupils in the eye) and movement (skeletal muscle). It diverts blood flow away from the GIT and skin via vasoconstriction. Blood flow to skeletal muscles, lungs is not only maintained, but enhanced (by as much as 1200%), in case of skeletal muscles. THE SYMPATHETIC NERVOUS SYSTEM Dominance by the sympathetic system is caused by physical or emotional stress “E situations” Emergency, Embarrassment, Excitement, Exercise Alarm reaction = flight or fight response: Dilation of pupils Increase heart rate, force of contraction & BP Decrease in blood flow to nonessential organs Increase in blood flow to skeletal & cardiac muscle Airways dilate & respiratory rate increases Blood glucose level increase THE PARASYMPATHETIC DIVISION The parasympathetic nervous system has "rest and digest" activity. Concerned with conservation and restoration of energy, as it causes a reduction in heart rate and blood pressure, and facilitates digestion and absorption of nutrients, and consequently the excretion of waste products The chemical transmitter at both pre and postganglionic synapses in the parasympathetic system is Acetylcholine (Ach). THE PARASYMPATHETIC DIVISION Enhance “rest-and-digest” activities Normally dominate over sympathetic impulses SLUDD type responses: salivation, lacrimation, urination, digestion & defecation 3 “Decreases” decreased HR, diameter of airways and diameter of pupil • Paradoxical fear when there is no escape route or no way to win causes massive activation of parasympathetic division loss of control over urination and defecation THE AUTONOMIC NERVOUS SYSTEM Acetylcholine activates mainly two types of receptors. They are called muscarinic and nicotinic receptors. Muscarine activates only muscarinic receptors whereas nicotine activates only nicotinic receptors; acetylcholine activates both of them. Muscarinic receptors are found on all effector cells that are stimulated by the postganglionic cholinergic neurons of either the parasympathetic nervous system or the sympathetic system. Nicotinic receptors are found in the autonomic ganglia at the synapses between the preganglionic and postganglionic neurons of both the sympathetic and parasympathetic systems. THE AUTONOMIC NERVOUS SYSTEM Sympathetic exceptions) (adrenergic, with Parasympathetic (muscarinic) circulatory system cardiac output increases M2: decreases SA node: heart rate (chronotropic) β1, β2: increases M2: decreases cardiac muscle: β1, β2: increases contractility (inotropic) M2: decreases (atria only) conduction at AV node β1: increases vascular smooth muscle M3: contracts; α = contracts; β2 = --relaxes platelets α2: aggregates --- mast cells - histamine β2: inhibits --- M2: decreases THE AUTONOMIC NERVOUS SYSTEM Sympathetic (adrenergic) Parasympatheti c (muscarinic) β2: relaxes (major contribution); α1: contracts (minor contribution) M3: contracts pupil of eye α1: relaxes M3: contracts ciliary muscle β2: relaxes M3: contracts respiratory system smooth muscles of bronchioles nervous system THE AUTONOMIC NERVOUS SYSTEM Sympathetic (adrenergic, with exceptions) Parasympathetic (muscarinic) salivary glands: secretions β: stimulates viscous, amylase secretions; α1 = stimulates potassium cation stimulates watery secretions lacrimal glands (tears) decreases M3: increases kidney (renin) secretes --- parietal cells --- M1: secretion liver α1, β2: glycogenolysis, gluconeogenesis --- GI tract motility decreases M1, M3: increases smooth muscles of GI tract α, β2: relaxes M3: contracts sphincters of GI tract α1: contracts M3: relaxes digestive system THE AUTONOMIC NERVOUS SYSTEM Sympathetic (adrenergic) Parasympathetic (muscarinic) pancreas (islets) α2: decreases secretion --- adrenal medulla N: secretes epinephrine --- bladder wall β2: relaxes contracts ureter α1: contracts relaxes sphincter α1: contracts; β2 relaxes relaxes sweat gland secretions M: stimulates (major contribution); α1: stimulates (minor contribution) --- arrector pili α1: stimulates --- ENDOCRINE urinary system THANK YOU